Matrix-type liquid crystal display devices in which thin film transistors (TFTs) are employed as switching elements are widely used as flat-panel television sets, display devices for personal computers, display devices for video imaging devices, and so on. In addition to conventional TN-type liquid crystal display devices, liquid crystal display devices of the VA (Vertical Alignment) mode, which is a vertical alignment mode, the IPS (In-Plane-Switching) mode, which is a lateral electric-field mode, and the like are being developed.
Known VA mode liquid crystal display devices are: liquid crystal display devices of the MVA (Multidomain Vertical Alignment) mode, each of whose pixel includes a plurality of domains with mutually different liquid crystal alignment directions; liquid crystal display devices of the CPA (Continuous Pinwheel Alignment) mode, in which gradually varying liquid crystal alignment directions exist around a rivet or the like that is formed on an electrode at the central portion of a pixel; and the like.
After a predetermined signal voltage is applied to a pixel electrode and until a new signal voltage is applied to this pixel electrode, a TFT remains in an OFF state because no scanning signal for placing the TFT in an ON state is applied to the gate of the TFT. In an unselected-period during which the TFT is in an OFF state, the potential of the pixel electrode is kept substantially constant, thus maintaining the displaying in accordance with this potential.
It has conventionally been known to provide a storage capacitor in parallel to the liquid crystal capacitor, the storage capacitor allowing the potential of a pixel electrode to be retained. Patent Document 1 shows an implementation in which a storage capacitor is formed between an extension of a drain electrode and a storage capacitor electrode (storage capacitor bus line). The extension of the drain electrode is provided so as to overlap the storage capacitor electrode in a region which is inside of the edge (outer edge) of the storage capacitor electrode. Moreover, in this display device, the storage capacitor electrode extends in a manner of overlying an end of the pixel electrode, such that a storage capacitor is created also between the pixel electrode and itself.
Patent Document 2 discloses a technique of creating a storage capacitor by forming, in a region inside the outer edge of an underlying conductive connection line, an overlying conductive portion via an insulating film. The reason why it is formed inside the edge of the underlying connection line is that, if the overlying conductive portion were provided in a manner of intersecting the edge of the underlying connection line, there would be an increased likelihood of current leakage or electrical conduction occurring at this intersecting portion.
Patent Document 3 describes, as a technique of providing a storage capacitor without lowering the aperture ratio of the pixel, forming a storage capacitor line and a storage capacitor electrode in an interspace between a plurality of subpixel electrodes. In this document, too, it is recited that a storage capacitor electrode extending from a drain electrode is provided inside of the edge of an underlying storage capacitor line.
Patent Document 4 and Patent Document 5 also describe liquid crystal display devices in which an extension of the drain electrode of a TFT is provided opposite from a storage capacitor bus line (Cs bus line). The extension of the drain electrode functions as a Cs counter electrode, and creates a storage capacitance between itself and a storage capacitor line, via an insulating film.
Moreover, in the liquid crystal display devices described in Patent Document 4 and Patent Document 5, the portion extending from the drain electrode extends beyond the underlying storage capacitor line. This extension is utilized as a control capacitor electrode, and constitutes capacitive coupling with a subpixel electrode which is in a floating state. To the subpixel electrode in a floating state, a potential which is different from that of another subpixel electrode which is directly connected to the drain electrode is applied via a control capacitor electrode. Such a method of applying different voltages to the two subpixel electrodes included within one pixel is known as a method of pixel division. By introducing liquid crystal regions with different alignment states in one pixel, the viewing angle characteristics can be improved.